Triodanis perfoliata (Clasping-leaved Venus' Looking-glass)

Plant Info
Also known as: Clasping Venus' Looking-glass
Family:Campanulaceae (Bellflower)
Life cycle:annual
Habitat:part shade, sun; dry sandy or rocky soil; prairies, roadsides, grassy slopes, rock outcrops, gravel pits, open woods
Bloom season:May - July
Plant height:4 to 30 inches
Wetland Indicator Status:GP: FAC MW: FAC NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 5-petals

[photo of flowers] One to 3 stalkless flowers in the leaf axils all along the elongating stem, with a few flowers open near the tip of the stem and fruit forming below. Flowers on the lowest part of the stem are small, self-fertile, petal-less and do not open (cleistogamous) while the upper flowers are more showy. The showy flowers are about ½ inch across with 5 elliptic petals fused at the base into a short tube. Protruding from the center is a white style with a 3-lobed tip, surrounded by 5 shorter stamens. Petal color ranges from deep blue-violet to pinkish-purple to pale lavender. The calyx cupping the flower has (usually) 5 hairless, narrowly triangular lobes shorter than the petals that have a long taper to a sharply pointed tip; cleistogamous flowers may have only 3 or 4 lobes.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are alternate along nearly the full length of the stem, up to 1 inch long and nearly as wide, broadly egg-shaped to heart or kidney-shaped, rounded to somewhat pointed at the tip, stalkless and usually clasping the stem at the base. Edges are usually coarsely toothed, sometimes toothless; surfaces are variably covered in stiff hairs though the uppermost leaves may be hairless. Stems are angled, stiffly hairy along the angles, unbranched or branched near the base, and mostly erect.

Fruit: Fruit type: capsule/pod

[photo of developing fruit] Fruit is a 2 or 3-sectioned, oblong-elliptic capsule with the persistent calyx lobes spreading out at the tip. Capsules are up to 3/8 inch long, with those of cleistogamous flowers about half that. As fruit matures, a hole (pore) develops at about midpoint on each capsule section; when seed is ripe the capsule splits from the top down to the pore and releases the seed. Seeds are numerous, about .5mm long, lens-shaped, shiny reddish-brown.


Clasping-leaved Venus' Looking-glass, formerly Specularia perfoliata, is native but considered weedy in some parts of its range, where it may pop up in sidewalk cracks, empty lots, and other disturbed areas. In Minnesota, it is typically found in rock outcrops and open sandy prairies, less often roadsides, gravel pits and grassy banks. While references note it may reach heights of 3 feet, 1 to 2 feet is more common. Some references list two varieties (or subspecies) of Triodanis perfoliata while others consider these separate species; these are T. biflora (var. biflora) and T. perfoliata (var. perfoliata). Minnesota is currently among the splitters and recognizes these as separate species.

T. biflora is generally a more southern species, its leaves more oval-elliptic and not clasping, and the pore on its fruit is near the tip of the capsule, not midpoint. Another similar species, Triodanis leptocarpa, only found in a single location in Dakota County in the 1930s and now considered historical, has more lance-elliptic leaves much longer than wide.

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More photos

Photos by K. Chayka taken in her garden. Photos courtesy Peter M. Dziuk taken in Chippewa, Renville, Rock and Scott counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Cass Markovich - NE Minneapolis
on: 2020-10-01 00:42:28

This appeared in my garden so I am trying to find out if it is invasive.

Posted by: K. Chayka
on: 2020-10-01 06:56:15

Cass, this is a native annual species and only reproduces by seed, and as the Notes mention, can volunteer in disturbed soils such as gardens. It is not very aggressive. If you don't want it in your yard, just pull it up to prevent it from producing any more seed.

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